It is well-known that a wide variety of phospholipid membranes of artificial and natural origin undergo reduction in their molecular ordering when exposed to general anesthetic agents. It has been suggested that this "fluidization" causes a change in the environment of the integral membrane proteins sufficient to alter their normal activities, and that such effects, in nerve cell membranes, may be partially responsible for the pharmacologic actions of these agents. The purpose of this research is to search for a mechanical basis for this lipid-protein coupling. We are currently engaged in studies of changes in the volume occupied by membrane-bound receptors isolated from the electric organ of Torpedo californica, an electric skate, when they are exposed to cholinergic ligands and general anesthetic agents. These measurements are being made using a sensitive interferometric bellows dilatometer.